Process for the drying of negative electrode plates



June 15, 1965 F. SUNDMAN 3,189,484

PROCESS FOR THE DRYING OF NEGATIVE ELECTRODE PLATES Filed July-27, 19642 Sheets-Sheet 1 I a; firmmm'i CD ll! '.I|I|1' H n :i i u 1o-- W k 14 uu (I L) i In Er FO/ke Subs/7x mry fl June 15, 1965 Filed July 27, 1964F. SUN DMAN PROCESS FOR THE DRYING OF NEGATIVE ELECTRODE PLATES Fig.2

2 Sheets-Sheet 2 tet 3,189,484 Patented done f5, 1965 3,189,484 PRGCESSFQR THC BRYHJG 6F NEGATiVE ELECTR'QDE PLATES Follre Snndmw, Hnltsfred,Sweden, assignor to Boiiden Airtiebclag, a company of Sweden Filed Juiy27, 196 5, Ser. No. 33%,118

Gaines priority, application Eiweden, San. 14, 196%, 327/69 1 Claim.(Cl. 136-33) T his application is a continuation-in-part of applicationSerial No. 13,372 filed March 7, 1960, now abandoned.

The present invention pertains to a process for the drying of negativeelectrode plates for a lead accumulator of the dry-charged typeretaining water following the forming process.

Such negative electrode plates are usually manufactured by first shapingand pasting a grid with lead oxide and then subjecting the plate thusformed to a special electrolytic reduction process in the presence of anaqueous solution of sulfuric acid, whereby the lead oxide is reducedinto a highly active finely divided lead metal in the form of sponge.Following this electrolytic treatment, the electrode plate is washedwith water to remove the sulfuric acid retained in the pores of theelectrode.

More particularly, the invention is concerned with a process forremoving this water by a drying process, in which the electrode plate ismaintained immersed in a bath consisting of a treament liquid no morethan slightly miscible with water While heating this bath to asufficiently high temperature to expel the water from the electrode andto substitute treatment liquid therefor and in which this treatmentliquid is then evaporated with formation of a protective layer on theelectrode plate.

Such a process is described in the U.S. Patent 2,747,008. '3

According to this process the negative electrodes to be dried aresuspended in a container, whereupon a treatment liquid consisting of asolution of a diflicultiy volatile substance in kerosene is introducedinto the container to form a bath surrounding the electrodes. This bathis then heated to a suficiently high temperature to expel the Water andsubstitute treatment liquid therefor. The bath is then removed from thecontainer, whereby, due to the own heat of the electrode, the volatileportion of the treatment liquid evaporates partially. -The remainingportion of the kerosene retained by the electrode is then removed bypermitting a hot gaseous medium to pass outside the flat sides thereof.After the evaporation of the kerosene, there will be left back aprotective layer consisting of the diificulty volatile portion of thetreament liquid. I have subjected electrode plates freed from water andprovided with a protective layer in this manner to certain tests. Inthis connection, it has been found, on the one hand, that, in a plane atright angles to the fiat sides of the electrode, the protective layer isdistributed in such a way that the concentration of the agent is thesame throughout the whole mass of the electrode, and, on the other hand,that in planes in parallel with the fiat sides the concentration of theprotective agent is higher in the lower portion of the electrode platethan in the upper portion thereof, the term lower being used to indicatethat or those parts of the electrode winch were on the lowest level inthe bath treatment and the term upper that or those parts which were onthe highest level. For

the experiments used a solution of parafiin in kerosene as a treatmentliquid and so-called double electrodes, the lower part of this electrodebeing thus that part of the electrode which was immersed most deeplyinto the bath of treatment liquid.

In order to test the ability of the active mass of the dried electrodereadily to get in effective contact with the electrolyte in connectionwith charging an accumulator or" the dry-charged type with sulfuricacid, a drop of an aqueous solution of surfuric acid having the specificgravity 1.28 was placed onto the surface of the electrode to be tested,whereupon the time which is consumed before the drop was disappearedinto the active mass was measured. Concerning the upper part of thedouble electrode, it

was found that, after treating the electrode to remove the kerosene withhot air for 5 minutes, this period of time amounted to, on an average,0.50 minute, corresponding value for a treatment period of 8 minutesbeing, on an average, 0.52 minute. Concerning the lower part of thedouble plate, the corresponding values were found to be 435 minutes fora hot air treatment time of 5 minutes and 1.40 minutes for a hot airtreatment time of 8 minutes.

The difference in result from the test above referred to is thus verysignificant. It can be explained in such a way that, after the removalof the treatment liquid from the electrodes, the treatment liquidretained by them will flow downwardly under the influence of the gravityforce through the electrode to collect in the lower portion thereof inthe same way as takes place when clothes from the wash are suspended toget dried. The lower portion of the clothes will be dried much moreslowly than the upper.

Furthermore, it has been found that the electrodes obtained according tothe known process suffer from the disadvantage that, seen in a directionat right angles to the fiat sides of the electrodes, the concentrationof the protective agent is constant throughout the whole active mass,which in turn means that the interior of the plate obtains too aneffective protection while the surface particles, which are most exposedto the influence of the atmosphere, obtained a reduced protection.

To sum up, the known process thus results in two disadvantages. The mostsevere one of these has proved that which is ascribed to the protectiveagent being differently distributed in the lower and upper parts thereofas evidenced by the drop test above referred to.

1 have found that these two disadvantages are removed or essentiallydiminished, if, in the process above referred to, the electrode platefreed from water is maintained immersed in a second bath consisting of asolution of a material capable of forming a protective coating orimpregnation on the electrode in a volatile liquid not or no more thanslightly miscible with water, whereupon the volatile liquid used as asolvent in the coating or impregnating process is evaporated togetherwith the remaining treatment liquid from the water expelling process.

The most important result of the modified process according to theinvention is that the electrode plate has its protective agent uniformlydistributed in planes in parallel with the flat sides of the electrodeplate.

In order to verify this result I have subjected the same doubleelectrode plates as above identified to the process according to theinvention. The process conditions were exactly in agreement with what isset forth under Example 1 below. It could be established, by the aqueoussulfuric acid drop test'with respect to the upper part of the doubleplate, that the period of time before the drop disappeared into theactive mass was, on an average, 0.18 minute, While the correspondingvalue concerning the lower part of the double electrode plate was 0.19minute, which indicates an almost exact agreement regarding the propertyin question.

The effect can be explained in the following manner: After taking up theelectrode freed from water from the kerosene bath, part of the liquidretained by the electrode evaporates at the same time as, due to thegravity force, the remain ng kerosene of the electrode will beconcentrated to the lower part. In dipping the electrode vention iscarried 'out' in three stages.

first stage of the drying process of theinvention, the water1removingprocess, the latter may preferably be plate in the second bathconsisting of a solution of paraffin in kerosene, the upper part of theelectrode will receive comparatively more solution. However, aftertaking up the electrode plate from the bath and most probbe equalizedthroughout the active mass.

-As,indicated above, the process according to the in- In respect of thecarried out in such a way as to transform the whole amount of the waterpresent in the electrode after forming and washing into the vapor form.In this connection, it is proper to maintain the electrode immersed in abath of the treatment liquid not dissolving water to any appreciabledegree, heat being supplied to the bath through heating'elementstherein, either in the form of stearn'or electrically. As a treatmentliquid is used a liquid the predominating 'part of which boils ata'temperature substantially in excess of 100 C., the boiling point ofwater, such as gasoline, white turpentine, kerosene, esters, ethers,ketones and the like, the water vaporized being condensed anddischarged. In order to diminish the fire hazardit is also possible touse a non- 1 combustible treatmentliquid, e.g. belonging to the class ofchlorinated hydrocarbons such as carbon tetrachlo- Jride,.trichloroethylene or perehlorethylene. In practice it has been foundthat hydrocarbons boiling between the limits of 150 and 200 C.,accordingto Engler, are very suitable for the purpose of driving oil theWaterpresent in accumulator electrodes after forming. ,Also kerosene hasproved satisfactory for this purpose. It has proved that the water ispractically completely driven ofi from V the electrode at a bathtemperature between 120 and 130 C. If a hydrocarbon fraction is used,the lower 1 boiling portions of which may be vaporized in the drivingonprocess, the hydrocarbons are separated from the waterafter'condensation'and returned to the bath. For the complete removal of thewater from the electrode I a treatment time of about 2-5 minutes, isrequired.

The electrode plate has now been freed from its water including thewater capillary bound and is then to be provided with the protectingagent. The purpose of this agent is to prevent that the particles ofactive'mass of the electrode will be attacked by the oxygen and themoisture of the atmosphere'during the period in storage.

The impregnating process 'is carried out by dipping.

In this process, the protective agent is applied in the 'form of asolution. of dissolving the protective agent may be used, it, however,being necessary that the solvent is a liquid in which ,Water is no morethan slightly soluble. It is proper to In principle any solvent capableuse the same solvent for the protective agent as for expelling the waterfrom the formed electrode plate in the first stage.

As a protective agent for theelectrode should be men a tioned productson the basis of mineral oil such as lubricating oil fractions, parafiinwax, asphalt as well as natural and synthetic vresins and plastics forexample polyethylene, water repelling salts etc. The protective agentmay a either be a substance liquid at room temperature or preferably asubstance solid at the normal'temperature of the atmosphere. Aspreferred examples of protective agents should be mentioned substanceshaving a'melting point in excess of -35 C., for example paraflin wax,

which has usually a composition as to meltat a temperature above C,

Suitable protective agents are paraffin wax, parafl'in oil, castor oiland so-called yolk (also called suint, an

'unctuous secretion of the skin of sheep), although many othersubstances selected for instance from 'the classes .mineraloils, animalfats, vegetable ofls, waxes and natural or synthetic resins may beuseful. The protective coating may also be provided by applying one ormore polymerizable substances which are caused to polymerize during theheat treatment necessary for driving off the treatment liquid used forremoving the water in the first stage.

Preferred amounts of the protective agent present in the impregnatingsolution applied. to the electrode freed from Water are 10400,preferably 10-30 g. of protective agent, for instance, paraflin wax ofthe melting point out by dipping the electrode/plate in 'a cold solution(temperature not exceeding 50 C.) of the protective agent for a periodof time in the range of from 10 sec. to 10 min. The conditions used forapplying the protective agent for the electrode plate may easily becontrolled to impart a maximum of protective eifect'to the electrodeplate without any essential decrease occurring in respect of theability, of the electrolyte rapidly to get in an intimate contact withthe active mass of the electrode.

After the protective agent has been supplied. to the electrode plate thelatter issubjected to a drying process to drive off the treatment liquidand the solvent used for the protective agent. This drying of theelectrode is most preferably eifected by hot air but also other gaseousV mediums such as carbon dioxide may be used. 7

The temperature used for driving off the treatment liquid from theelectrode plate depends on 'the boiling point or boiling point intervalof the treatment liquid. It kerosene or mineral spirit is used as atreatment'liquid and as a solventfor 'the protective agent suitabletemperatures for the driving-off process are in the range of from to 190C., preferably 'in the range from to C. However, also temperatures below150 C. may be used in extreme cases. Temperatures above C. may be usedin certain cases, if a treatment liquid at least mainly consisting ofhigh boiling components is used for the removalof the water in the firststage. The

temperature used for driving off the treatment liquid must not be sohigh as to cause changes in the structure of the lead. In practicetemperatures in excess of 250 C. are not suitable in view of thesepossible changes.

A very important advantage of the present process is:

driving-off the treatment liquid from the electrode plate as rapidly aspossible (3-12 min.) For sanitary purposes it may be preferable to coolthe electrode plate in a closed chamber also serving as a sluice beforetaking it out of the drying apparatus.

An apparatus for drying formed negative electrode plates may comprise afirst vessel adapted to contain a bath consisting of a treatmentliquidnot more than slightly soluble in water, heating means in said vessel tokeep the temperature of said bath sufiiciently high to drive off a thewater retained by the active mass of the electrode after forming andwashing, a second vessel adapted to contain an impregnatingsolutioncomprising a protecting agent for the electrode, cooling'means in thisvessel to keep the temperature of the bath'below 50 C.', a drying 1chamber provided with heatingmeans for a drying medium passing aroundthe electrodesto drive oil the treatment liquidand the solvent used forthe protecting agent;

the vessels and drying chamber being connected with each other in seriesby passages arranged therebetween, means for closing and opening thesepassages, basket elevators arranged in these vessels, respectively,adapted to contain crates with electrode plates, these crates beingsupported by rolls attached to these basket elevators, and fixed rollsarranged each in the passage between the two vessels, in the passagebetween the second vessel and the drying chamber, the fixed rolls andthe rolls attached to the basket elevators, respectively, forming a pathinclining in a direction from the first vessel to the drying chamber,the arrangement enabling the drying process to be carried outsemicontinuously.

This apparatus will now be described more in detail with reference tothe enclosed drawing.

FIGURE 1 is a view of the bath containers.

FIGURE 2 is a view of the drying chamber.

The apparatus used for the drying process above referred to thusconsists of two vessels or containers, the first of which 1 is adaptedto receive a bath consisting of kerosene as a treatment liquid and thesecond one 2 of which is adapted to receive a bath 11 of an impregnatingsolution consisting of the same kerosene as a solvent and parafiin waxdissolved therein. Connected to the latter container 2 is a chamber 3 inwhich the electrodes treated in container 1 and impregnated in container2 are to be freed from kerosene. To the drying chamber 3 is a coolingchamber 4 connected, wherein the dried electrodes are to be cooledbefore being taken out of the drying apparatus. Above the bottom ofcontainer 1, in the vicinity thereof, heating elements 5 are arranged tomaintain-the temperature of the kerosene bath at a sufficiently hightemperature to cause an evaporation of the water present in theelectrodes to be treated. In the container 2 holding the bath ofimpregnating solution a cooling tube 6 is arranged to keep thetemperature of the bath at a temperature below 50 C. in the impregnationof the electrode plates freed from water in the container 1. On the topor" the drying chamber 3, there is a fan 7 arranged to conduct a streamof hot air around the electrodes to remove the solvent used for theimpregnating process. This air is first passed around heating elements12 in the bottom of the chamber from an inlet (not shown) and the spentdrying air containing the vapors of solvent is passed out from thedrying chamber through an outlet duct'at the top of the chamber, towhich tube the fan 7 is connected to the shaft of the fan (not shown) ina manner obvious to any one skilled in the art.

in the container 1 there is arranged an elevator basket 8. This basketis adapted to contain a crate 9 with electrodes. This crate is supportedby rolls 13 attached to the basket, which latter can be elevated andlowered by actuating a piston adapted to slide in a tube by a pressuremedium, such as compressed air or a pressure liquid. During itsmovement, this piston causes the basket to move either upwardly ordownwardly by actuating two ropes 15 and 16, respectively, supported bysuitable fixed break rolls 17. The container 1 is provided with anoutlet 18 connected to a cooler (not shown) for the water driven offduring the dewatering process.

In the container 2 the means for elevating and lowering the basket 19 upfrom and down into, respectively, the bath i1 correspond to the meansused in container 1. Container 1 and container 2 are connected with eachother through a connection tube 2%), which can be closed and opened by amechanically operated swingable gate 27.. The swinging movement ishereby effected by actuating a piston adapted to slide in a tube 22 bypressure medium. The container 2 and the drying chamber 3 are connectedwith each other through a second connection tube 23 adapted to be closedand opened, respectively, by a mechanically operated gate 24. This gateis elevated and lowered by a piston the movement of which is effected bypressure medium. The cooling tube 4 connected to the drying chamber 3 isprovided with a swingable gate 25 which is mechanically operated in themanner above referred to with reference to the gate 21. There is alsoprovided a swingable gate 26 at the end of the cooling tube 4, this gatebeing arranged to open and close the cooling tube when treatedelectrodes are to be taken out of the drying apparatus.

*From the outlet end of the container 2 to the outlet of the coolingtube 4 there is arranged a path of fixed rolls 27. The rolls attached tothe elevator basket 8 of the container 1 the fixed rolls 27 in theconnection tube 20, the rolls 28 attached to the elevator basket 19 ofcontainer 2 and the rolls 27 above referred to form a rolling path whichis inclined downwardly in adirection from the first container 1 to thecooling tube 4. Hereby the crate with electrodes can easily be passedsuccessively through the different treatment units consisting ofcontainer 1 (the dewatering stage), container 2 (impregnating stage),the chamber 3 (drying stage) and the cooling tube 4, respectively, byits own gravity. Special stop means (not shown) are arranged in thecontainers 1 and 2, respectively, in the drying chamber 3 and in thecooling tube 4 to prevent non-intended movement of the basket 8 duringits retention in the different treatment vessels. These stop means areof course to be operated from the outside of the apparatus.

The apparatus is preferable insofar as it enables a semicontinuousoperation of the drying process.

EXAMPLE 1 A number of formed lead electrode plates for a motor carbattery, containing water (about 10 ml. per plate) from the washingprocess following the reduction process to remove sulfuric acid isplaced in the crate 9 and dipped in the bath 16 consisting of kerosene,which has been preheated to a temperature of C. The bath is then haetedby the heating elements sufiiciently to expel the water from theelectrodes (120-130" C.). The water leaving the electrode andaccompanying small amounts of light hydrocarbons from the kerosene arecondensed in a cooler, the hydrocarbons being returned to the bath.

The electrodes are then taken up from the bath by elevating the basket 8and then allowed to roll through the tube 20 on the rolls 27 to theelevator basket 1? of container 2. This container holds an impregnatingsolution consisting of kerosene with paraffin wax dissolved therein inan amount of 36 g. per liter of solution. Th electrodes are immersed inthis bath for 5 min. at a temperature of 40 C. after which theelectrodes are subjected to a temperature of C. in the drying chamber 3to drive off the kerosene with which the electrodes have been soakedduring the dewatering and impregnating steps. After the kerosene hasbeen removed the plates are allowed to cool in the cooling chamber 4,whereupon they are taken out from the drying apparatus.

The electrode plates thus treated was examined on distribution ofpar-afi'in wax by the method described beneath. Hereby it was found thatthe paratfin wax had been uniformly distributed throughout the plate,seen in planes in parallel with the flat sides, but seen in a directionat right angles to the flat sides of the electrode plate, thedistribution of protection agent was such that the concen tration washigher at the surface and that in the middle part.

EXAMPLE 2 For this purpose a pack of electrodes is treated to removedwater in the same way as described in Example 1. The electrodes freedfrom water retaining kerosene having a temperature of about 120 C. arethen impregnated by rapidly dipping them in a kerosene solution ofparaflin (30 g. per liter) for 3 min. at a temperature of 26 C. and thensubjecting them to hot air at a temperature of 180 C. to remove thekerosene.

The electrode plates were examined on distribution on parafiin by themethod described beneath. In this connec-tion, it was found that theparaifin, as in Example 1, had been uniformly distributed throughout theplate, seen in planes in parallel with the flat sides of the electrodeplate, but seen in a direction at right angles to the flat sides of theplate, which had a thickness of 2 mnr, its distribution was such thattheconcentration of paraifin wax was considerably higher at the surfacethan in the middle part ithereof. The total amount of paraflin; wax inthe plate which Weighed'ZOO g. was found to be 50 mg.

According to the invention it is possible to obtain an impregnationwhich although requiring a smaller amount ofirnpregnating agent than theplates known up to now "excellently protects the electrode plate againstoxygen and j moisture during the time in storage and which is moreeasily decomposed, forced away or broken through bythe electrolyte thanknown impregnations. The amount of protective agent necessary to obtaina satisfactory protective efiect in an electrode plate can be diminishedby about 25%; The amount of organic materialintroduced into the batteryin the form ofthe protective agent can thus be kept lower. 7

j 'Whatlclaim is:

A method for the drying and coating'of a negative electrode plate forlead accumulators of the dry-chargedtype, which plate contains waterfollowing the forming process, comprising (1) suspending said plate ina'bath consisting of a treatment liquid which is 'no more than slightlymiscible with water, said liquid boiling at a temperature high-. er thanthe boiling point of water and being substantially free of difficultyvolatile material, i V

(2) heating said bath to a sufficiently high temperature to expelsubstantially all of the water, from said plate by evaporation and tosubstitute said treatment liquid for said water,

(3) removing said plate from said treatment liquid,

suspending said plate and permitting partial drying I thereof byself-contained heat,

(4) suspending said plate in a second bath consisting of a solution ofsubstantial amounts of diificulty volatile material in a volatilesolvent not miscible with water but miscible with said treatment liquid,

whereby the upper parts of said plateireceive comparatively more of saidditticulty volatile material 7 than the lower parts, and e l p-(5)'removing said plate from said second bathand evaporating saidvolatile solventso that said solution of difi iculty volatile materialin a solvent not miscible with Water absorbed by said plate flowsdownwardly t following said second bath and in the evaporating processto distribute uniformly throughout the active mass of said plate, seenin directions parallel with the flat sides of thet latter.

References Cited by the Examiner UNITED 'STAT PATENTS 2,747,008 5/56Sundb erg et'al; i,136 3 2,889,388 6/59 Csapo h 136-33 FQBEIGN PATENTS754,136 8/5 --Great Britain.

WINSTON A. DOUGLAS, Primary Examiner, JOHN H. MACK, Examiner.

